1. Field of the Invention
The present invention relates to brachytherapy devices, and more particularly to improved radioactive seeds for use in radiation therapy.
2. Discussion of the Related Art
Percutaneous transluminal coronary angioplasty (PTCA) is a therapeutic medical procedure used to increase blood flow through an artery and is the predominant treatment for coronary vessel stenosis. The increasing popularity of the PTCA procedure is attributable to its relatively high success rate and its minimal invasiveness compared with coronary by-pass surgery. Patients treated utilizing PTCA; however, may suffer from restenosis. Restenosis refers to the re-narrowing of an artery after a successful angioplasty procedure. Restenosis usually occurs within the initial six months after an angioplasty. Early attempts to alleviate the effect of restenosis included repeat PTCA procedures or by-pass surgery, with attendant high cost and added patient risk.
More recent attempts to prevent restenosis by use of drugs, mechanical devices, and other experimental procedures have limited long term success. Stents, for example, dramatically reduce acute reclosure and slow the effects of smooth muscle cell proliferation by enlarging the maximal luminal diameter, but otherwise do nothing substantial to slow the proliferative response to the angioplasty induced injury.
Restenosis is now believed to occur at least in part as a result of injury to the arterial wall during the lumen opening angioplasty procedure. In some patients, the injury initiates a repair response that is characterized by hyperplastic growth of the vascular smooth muscle cells in the region traumatized by the angioplasty. Intimal hyperplasia or smooth muscle cell proliferation narrows the lumen that was opened by the angioplasty, regardless of the presence of a stent, thereby necessitating a repeat PICA or use of other procedures to alleviate the restenosis.
Recent studies indicate that intravascular radiotherapy (IRT) has promise in the prevention or long-term control of restenosis following angioplasty. Intravascular radiotherapy may also be used to prevent or delay stenosis following cardiovascular graft procedures or other trauma to the vessel wall. Proper control of the radiation dosage, however, appears to be important to inhibit or substantially arrest hyperplasia without causing excessive damage to healthy tissue. Underdosing may sometimes result in inadequate inhibition of smooth muscle cell hyperplasia, or even exacerbation of hyperplasia and resulting restenosis.
Radiation therapy may also be utilized in the treatment of other diseases such as cancerous and non-cancerous tumors. In this type of therapy, the ultimate aim is to destroy the malignant tissue without causing excessive radiation damage to nearby healthy, and possibly vital tissue. This is difficult to accomplish because of the proximity of malignant tissue to healthy tissue.
Brachytherapy is a form of radiation treatment in which an ionizing radiation source is placed into or adjacent to a tumor or stenotic lesion. Although any number of radioactive substances and/or radioactive sources may be utilized in brachytherapy, Iodine-125 is currently a good candidate isotope for vascular brachytherapy. Iodine-125 has been used as a liquid or immobilized onto a variety of surfaces for diagnostic and therapeutic purposes. It has already been fashioned into a variety of shapes and used clinically for cancer treatment as briefly described above. One standard method for immobilizing Iodine-125 on to a solid surface is through electroplating. Currently, Iodone-125 is immobilized onto the surface of solid silver wires for a very secure bond. Silver is specifically utilized because of the extremely secure bond it forms with the Iodine-125. In order to ensure the effectiveness of the radiation, the entire radioactive source should contribute photons of radiation. However, in this design, a number of photons produced on one side of the seed or wire may have to travel through the solid stiver wire to be a component of the radiation dose on the other side of the wire or the seed. A difficulty with this is that the solid silver wire attenuates some of these photons that are produced by the Iodine-125 plated on the surface of the silver wire thereby reducing the therapeutic effectiveness. In addition, standard seeds or wires currently utilized have minimal surface area due to size constraints, thereby also reducing the radiation dose.
The low attenuating radioactive seed design of the present invention provides a means for overcoming the difficulties associated with the treatments and devices as briefly described above.
In accordance with one aspect, the present invention is directed to a radioactive seed. The radioactive seed comprises a core having an outer surface and a radioactive material attached to the outer surface of the core. The core has a predetermined length and multifaceted cross-section.
In accordance with another aspect, the present invention is directed to a low attenuation radioactive seed. The low attenuation radioactive seed comprises a core having an outer surface, a substrate affixed to the outer surface of the core, and a radioactive material attached to the substrate. The core has a predetermined length and a multifaceted cross-section.
In accordance with another aspect, the present invention is directed to a low attenuation radioactive seed. The low attenuation radioactive seed comprises a hollow core having an inner surface and an outer surface, and a radioactive material attached to at least one of the inner and outer surface of the hollow core. The hollow core has a predetermined length and a multifaceted cross-section.
The low attenuating radioactive seeds of the present invention utilize modified cross-section wires to increase the surface area upon which the radioactive substance may be deposited without increasing the overall size of the seed. In addition, the modified cross-section wires are designed in such a manner as to reduce the distance a photon directed inwardly rather than outwardly would have to travel through the wire, thereby reducing attenuation. Accordingly, the low attenuating radioactive seeds will have increased dose rates, decreased dwell times because of the increased dose rates, and improved clinical outcomes by increasing the dose consistency throughout the treatment zone.
The low attenuating radioactive seeds of the present invention comprise a silver wire or silver-plated metallic or non-metallic wire that has a fluted or non-circular cross-section. The wire may be plated with Iodine-125 or other radioactive isotope and used to deliver a therapeutic dose of radiation. The low attenuating radioactive seeds require minimal changes in manufacturing processes over existing seeds, thereby minimizing any significant increases in manufacturing costs. In addition, given that the overall size of the seed remains substantially unchanged, existing delivery devices may be utilized thereby obviating the need for redesigned delivery devices.